On my laptop, the 'Write speed dialog' is not useful - it contains multiple entries for every decimal speed between 0.0x and 18.1x. See http://bugzilla.gnome.org/show_bug.cgi?id=350082 This is fixed in nautilus-cd-burner-2.16.1.
Fedora Core 5 and Fedora Core 6 are, as we're sure you've noticed, no longer test releases. We're cleaning up the bug database and making sure important bug reports filed against these test releases don't get lost. It would be helpful if you could test this issue with a released version of Fedora or with the latest development / test release. Thanks for your help and for your patience. [This is a bulk message for all open FC5/FC6 test release bugs. I'm adding myself to the CC list for each bug, so I'll see any comments you make after this and do my best to make sure every issue gets proper attention.]
This was fixed in an update.